Field of the Invention
The present invention relates to an image forming apparatus configured to form an image on a sheet.
Description of the Related Art
Generally, in an image forming apparatus such as a copier, a sheet is sometimes laterally displaced in a width direction of the sheet while being conveyed. In the case where an image is formed on the sheet laterally displaced, the image printed on the sheet is displaced from the center of the sheet. This may be perceived as printing of a poor quality. Therefore, a shifting mechanism that detects the position of an edge portion of the sheet in the width direction and corrects the lateral displacement of the position of the sheet is known.
In Japanese Patent Laid-Open No. 2009-143643, an image forming apparatus that detects the position of an edge portion of a first page sheet in the width direction and corrects the image formation position for a third page sheet on a photoconductor on the basis of the amount of displacement of the edge portion of the first page sheet from a standard position is proposed. This image forming apparatus corrects the image formation position in advance on the basis of the amount of displacement of a sheet of two pages before, and thereby reduces the shift amount of the sheet to improve the image quality and the productivity of the image forming apparatus.
Generally, an image forming apparatus includes an image forming portion configured to form an image, a sheet feed portion configured to feed a sheet, and a duplex conveyance portion configured to convey the sheet on a first surface of which an image has been formed to the image forming portion again for forming images on both surfaces of the sheet. In addition, since the sheet may be skewed when a shifting mechanism shifts the sheet in a width direction in the case where the shift amount of the sheet is too large, an upper limit value of the shift amount is set. It can be considered that the upper limit value of the shift amount of the sheet by the shifting mechanism is set so as to vary depending on which conveyance path the sheet passes through. The upper limit value of the shift amount is set to vary because the length and shape of the conveyance path, arrangement of conveyance rollers in the conveyance path, and the like are different between the sheet feeding portion and the duplex conveyance portion.
Therefore, there is a case where, in an image forming apparatus disclosed in Japanese Patent Laid-Open No. 2009-143643, the shift amount of the sheet exceeds the upper limit value when forming an image on a first surface of the sheet and the shift amount of the sheet becomes equal to or smaller than the upper limit value when forming an image on a second sheet of the sheet. In this case, the precision of alignment of the image formed on the first surface is low, and the precision of alignment of the image formed on the second surface is high. This results in displacement of images between the first surface and the second surface of the sheet. In this way, there has been a difference between the relative positions of the images formed on the first surface and the second surface of the sheet, and this has been problematic for the quality of a printed product.